Residential circuit interruption is efficiently accomplished within residential circuit breakers containing a thermal-magnetic trip unit, an operating cradle and a pair of separable contacts. The thermal response is provided by means of a bi-metal element that is electrically-connected in series with the separable contacts for so-called "long time" current sensing and the magnetic response is provided by a stationary magnet that partially surrounds the bimetal and interfaces with a movable armature that carries the cradle retention latch for so-called "short time" current sensing. A good example of a residential circuit breaker including a thermal-magnetic trip unit is found in U.S. Pat. No. 4,513,268 entitled Automated Q-Line Circuit Breaker".
Various enhancements are available for enhancing the magnetic response and allowing short time protection at lower ampere ratings. One such enhancement is found in U.S. patent application Ser. No. 08/804,045 filed Feb. 21, 1997 entitled "Residential Circuit Breaker Having an Enhanced Thermal-Magnet Trip Unit".
Efforts to enhance both the thermal and magnetic response of low cost residential circuit breakers often result in a cost increase due to additional components and increased manufacturing time.
Accordingly, it would be economically feasible to enhance both the thermal and magnetic response within such residential circuit breakers without incurring a corresponding cost increase.
One purpose of the invention is to describe one such thermal-magnetic trip unit having enhanced thermal and magnetic response at a savings in both component cost and in manufacturing time.